From: Martin KaFai Lau <martin.lau@linux.dev>
To: Philo Lu <lulie@linux.alibaba.com>
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
andrii@kernel.org, eddyz87@gmail.com, song@kernel.org,
yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me,
haoluo@google.com, jolsa@kernel.org, xuanzhuo@linux.alibaba.com,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Add rcu ptr in btf_id_sock_common_types
Date: Tue, 8 Oct 2024 12:05:59 -0700 [thread overview]
Message-ID: <80cb3d4b-cebb-4f08-865d-354110a54467@linux.dev> (raw)
In-Reply-To: <20241008080916.44724-1-lulie@linux.alibaba.com>
On 10/8/24 1:09 AM, Philo Lu wrote:
> Sometimes sk is dereferenced as an rcu ptr, such as skb->sk in tp_btf,
> which is a valid type of sock common. Then helpers like bpf_skc_to_*()
> can be used with skb->sk.
>
> For example, the following prog will be rejected without this patch:
> ```
> SEC("tp_btf/tcp_bad_csum")
> int BPF_PROG(tcp_bad_csum, struct sk_buff* skb)
> {
> struct sock *sk = skb->sk;
> struct tcp_sock *tp;
>
> if (!sk)
> return 0;
> tp = bpf_skc_to_tcp_sock(sk);
If the use case is for reading the fields in tp, please use the bpf_core_cast
from the libbpf's bpf_core_read.h. bpf_core_cast is using the bpf_rdonly_cast
kfunc underneath.
pw-bot: cr
next prev parent reply other threads:[~2024-10-08 19:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-08 8:09 [PATCH bpf-next] bpf: Add rcu ptr in btf_id_sock_common_types Philo Lu
2024-10-08 19:05 ` Martin KaFai Lau [this message]
2024-10-09 2:23 ` Philo Lu
2024-10-10 22:07 ` Martin KaFai Lau
2024-10-11 1:46 ` Philo Lu
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